The present invention relates generally to laser cutting and more particularly, to the gas-assisted laser cutting of explosives and ordnance.
The demilitarization of millions of tons of unexploded ordnance (i.e. articles having an encased explosive charge) is a significant problem in the world today. There are currently two general approaches to demilitarization of ordnance. The first is open burning/open detonation (OB/OD) of the ordnance. The OB/OD approach ensures the destruction of the ordnance but is costly and environmentally intrusive. The second approach involves demilling the ordnance, i.e. cutting through the casing and removing the encased explosive and/or fuse. The demilling approach is generally preferred because it does not result in detonation, and the recovered explosive can be recycled or disposed of safely.
Laser-based demilling methods, both non-thermal and thermal, have been reported. U.S. Pat. No. 6,150,630 to M. D. Perry et al. entitled xe2x80x9cLaser Machining of Explosives,xe2x80x9d hereby incorporated by reference, describes a non-thermal method for machining explosives and demilling. According to this method, an explosive may be machined by irradiation with ultrashort (5 femtoseconds to 100 picoseconds) laser pulses at a high repetition rate (0.01 to over 100 kHz) at wavelengths of about 0.2-12 microns. Each laser pulse converts small portions of the explosive, typically an organic material such as TNT, RDX, and TATB, into ionized plasma with minimal energy loss and minimal shock to the remaining explosive. It is also reported that this method can be used to safely cut through munitions. It is, however, unlikely that this method would make a significant impact in reducing the current stockpile of munitions because of the much greater difficulty in cutting through the metal casing by converting the metal casing into ionized plasma in order to gain access to encased explosive.
Attempts at using thermal laser based cutting methods have been largely unsuccessful. Like the non-thermal method described above, thermal laser based cutting also involves irradiating portions of the munition casing with a laser beam. In contrast, thermal laser cutting methods use a much higher average power beam that easily melts/vaporizes the metal casing. After cutting through the casing, the beam contacts and heats a portion of the explosive. The temperature rise is so rapid that the ignition temperature is rapidly reached and before the beam can be deflected away from the explosive, deflagration and detonation occur.
In view of the dangers associated with the millions of tons of unexploded bombs, mines, detonators, and other ordnance, only rapid methods having a wide margin of safety will make a significant impact in reducing their number and associated dangers. Thus, rapid methods for demilling ordnance remain without detonation and deflagration remain desirable.
Therefore, an object of the present invention is to provide a rapid and relatively safe method of demilling ordnance without detonation and deflagration.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention includes a method for laser machining a mass of solid explosive. The method includes directing a laser beam to a surface portion of a mass of high explosive to melt and/or vaporize the surface portion, while directing a flow of gas at the melted and/or vaporized surface portion. The gas flow sends the melted and/or vaporized surface portion away from the charge of explosive that remains.
The invention also includes a method of splitting the casing of an article of ordnance having an encased explosive. The method includes directing a laser beam to a surface portion of the casing of an article of ordnance to melt and/or vaporize the surface portion. A stream of gas is directed at melted and/or vaporized surface portion to send the melted and/or vaporized surface portion away from the portion of the article of ordnance that remains. The relative position of the laser beam and the article of ordnance is changed until the laser beam splits the ordnance casing.
The invention also includes a method of cutting an article of ordnance having an encased solid explosive. The method includes directing a laser beam to a surface portion of an article of ordnance casing to melt and/or vaporize the surface portion. A stream of gas is directed at the melted and/or vaporized surface portion to send the melted and/or vaporized surface portion away from the portion of the article of ordnance that remains. The relative position of the laser beam and the article of ordnance is changed until the laser beam splits the ordnance casing. After the casing is split, the laser beam is directed to a surface portion of the encased solid explosive to melt and/or vaporize the surface portion of the solid explosive while directing the flow of gas at the melted and/or vaporized solid explosive to send the melted and/or vaporized explosive away from the portion of the article of ordnance that remains until the laser beam splits the encased solid explosive.